In general, heavy construction vehicles use hydraulic motors or engines as their power source, and are classified into wheel type and crawler type according to means of mobility.
Although a heavy construction vehicle is not intended to travel at a high speed and does not require multistage shifting, the heavy construction vehicle has essential concerns to be addressed such as reduction of noise and vibration transferred from an engine and minimization of radius of gyration.
FIG. 1 is a view showing a configuration of a conventional drivetrain, which is applied to a forklift truck as a kind of heavy construction vehicle. In such a conventional forklift truck, a transmission 1 is installed at its center region. A clutch 6 is disposed between an input shaft 2 and an output shaft 3 of the transmission 1, which is intended to cause turning force from the input shaft 2 to be cut off and to be transferred to the output shaft 3.
The clutch 6 is connected to a torque converter 5 which serves to augment driving force transferred from an engine 4 placed at a rear part of the forklift truck. The turning force transferred to the output shaft 3 of the transmission 1 is transferred to an axle shaft 9 through a final reduction gear 7 and a differential gear 8 to rotate wheels. An axle hub includes a drum brake or a disc brake (not shown) therein to brake on the moving vehicle.
However, the above-mentioned conventional transmission applied to a heavy construction vehicle such as a forklift truck has disadvantages in that there is a long distance between an engine and an axle shaft because the transmission together with a clutch are placed between a torque converter and an axle shaft, much of vibration and noise generated from the engine is transferred to a driver's seat located at the center of the heavy vehicle through the transmission, and it is difficult for a user to operate the heavy vehicle at a narrow site because the heavy vehicle must be configured to be long due to the transmission.
Since such a heavy construction vehicle, which is equipped with a transmission having a conventional configuration, turns in the same way as that of a usual passenger vehicle or a transport vehicle, the radius of gyration “R” of the heavy vehicle is relatively large, as shown in FIG. 2. Hence, it is difficult to operate at narrow site, and also its operating behavior is relatively slow.
Furthermore, a conventional heavy construction vehicle rearwardly moves when the vehicle begins to move from a stopped state on a slope way (when gear shifting is carried out). Since a heavy construction vehicle equipped with a transmission having a conventional configuration includes a large-sized housing adapted to receive a clutch and a transmission, there are drawbacks in that it is impossible to freely design the center part of the vehicle and it is possible to achieve a satisfactory reduction ratio only where a final reduction gear intended to finally reduce an engine speed is designed to have a large size.
To solve the above problems, the present applicant filed Korean Patent Application No. 2000–46795 titled “a wheel transmission for a heavy construction vehicle” which is adapted to be mounted on axle hubs of both front or rear wheels to prevent generation of noise from an engine and transfer of vibration to a transmission and is intended to drive the both wheels independently to minimize a turning radius of the vehicle. Furthermore, the wheel transmission in the application is intended to improve braking performance while integrally constituting a brake with a clutch, and is adapted to be compact to freely design an engine mounting and an axle mounting.
The wheel transmission is characterized in that in a wheel transmission for driving a pair of right and left wheels independently which includes a planetary gear assembly, a first change clutch part, a second change clutch part and a one-way clutch part housed in an axle hub at which opposite ends of an axle shaft are located, turning force from an engine of a heavy construction vehicle being transferred to the axle shaft through a torque converter, a driving shaft, a final reduction gear and a differential gear,                the planetary gear assembly includes a sun gear formed at an end of the axle shaft, and a plurality of planetary gears engaged with the sun gear and connected to one another via a carrier, the planetary gears being engaged with ring gears,        the first change clutch part includes a cylinder disposed in the axle hub positioned at a location corresponding to a radius of the ring gear in which the cylinder is provided therein with a brake piston and a service piston engaged with each other to be moved in the long direction of the axle hub by supply of hydraulic oil, the brake piston is elastically supported by a disc spring, the service piston is coupled to a reaction plate, and an inner surface of the axle hub and an outer surface of the ring gear are provided with a brake plate and a frictional plate engaged with each other in a spline manner to press the reaction plate,        the second change clutch part includes a cylinder disposed in the axle hub positioned at a location corresponding to a radius of the carrier in which the cylinder is provided therein with a brake piston and a service piston engaged with each other to be moved in the long direction of the axle hub by supply of hydraulic oil, the brake piston is elastically supported by a disc spring, the service piston is coupled to a reaction plate, and an inner surface of the axle hub and an outer surface of the carrier are provided with a brake plate and a frictional plate engaged with each other in a spline manner to press the reaction plate, and        the one-way clutch part includes a first one-way clutch through which an output shaft of the ring gear is connected to the wheel to cause the wheel to be rotated only in a reverse direction, and a second one-way clutch through which an output shaft of the carrier is connected to the wheel to cause the wheel to be rotated only in a forward drive direction.        
Moreover, this wheel transmission is characterized in that the torque converter is provided at an output shaft with a usual auxiliary clutch so as to cause turning force of an engine to be transferred to a drive shaft or to be not transffered.
Therefore, according to the above patent application, since the wheel transmission is installed at wheel axle hubs of both wheels of front wheels or rear wheels, a distance between an engine and an axle shaft can be reduced, vibration and noise generated from an engine can be intercepted, a heavy construction vehicle can be operated at a narrow site by reduction in a full length of an equipment, it is possible to minimize a turning radius of a heavy construction vehicle, the wheel transmission serves as a service brake (a brake actuated in a running state), a parking brake and a clutch, and it is possible to improve braking performance and durability by adopting a wet oiling brake.
Furthermore, since a wheel is stably locked by the one-way clutch, it is possible to prevent a heavy construction vehicle from moving rearward when being started up on a slope way.
In addition, it is possible to broaden design flexibility of an engine mounting and an axle mounting by affording extra space to the center portion of a heavy construction vehicle, since speed of an engine is finally decelerated by a gear ration of a planetary gear assembly, it is possible to achieve a sufficient gear ratio even though a final reduction gear is reduced in size, and braking operation is automatically achieved by restoring force of a disc spring when an engine is stopped and this hydraulic pressure is released.
The present applicant also filed a provisional patent application titled “a wheel transmission for a heavy construction vehicle”(Korean Patent Application No. 2001–11280) on the basis of the wheel transmission (Korean Patent Application No. 2000–46795), in which a sun gear is divided into a forward drive sun gear and a reverse sun gear, a ring gear is held on a housing, and wheels are independently rotated in forward drive direction or reverse direction by a drive of a carrier due to rotation of the forward drive sun gear and the reverse sun gear.
FIGS. 3 to 5b show a configuration of the wheel transmission (Korean Patent Application No. 2001–11280). More specifically, FIG. 3 is a cross-sectional view of the wheel transmission, FIG. 4a is an enlarged cross-sectional view of “A” portion of FIG. 3 in a forward drive travel, and FIG. 4b shows a planetary gear assembly in forward drive travel.
FIG. 5a is an enlarged cross-sectional view of “A” portion of FIG. 3 in a reverse travel, and FIG. 5b is a view showing a planetary gear assembly of FIG. 5a in a reverse travel.
As shown in the drawings, the wheel transmission (Korean Patent Application No. 2001–11280) is characterized in that in a wheel transmission 100 for driving a pair of right and left wheels 102 independently, which includes a planetary gear assembly 110, a first change clutch part 130 and a second change clutch part 140 housed in an axle hub 104 at which opposite ends of an axle shaft 108 are located, turning force from an engine being transferred to the axle shaft 108 through a torque converter, a driving shaft, a final reduction gear and a differential gear,                the planetary gear assembly 110 includes a pair of forward drive sun gear 114 and reverse sun gear 116 with the axle shaft 108 and a bearing 112 disposed therebetween in which the forward drive sun gear 114 is engaged with a plurality of first planetary gears 120, and the reverse sun gear 116 is engaged with a second planetary gear 122 with which a first planetary gear 120, the first planetary gear 120 being engaged with a ring gear 124 fixedly placed at an axle housing 106,        the first change clutch part 130 includes a cylinder 132 disposed in the axle hub 104 positioned at a location corresponding to that of the forward drive sun gear 114 in which a forward drive piston 136 advances and comes into close contact with the forward drive sun gear 114 while compressing a return spring 138 by supply of hydraulic oil into the cylinder 132, and at the same time a clutch plate 135 disposed at the forward drive sun gear 114 comes into close contact with a frictional plate 137 provided at a first clutch pack 108a extended from the axle shaft 108 so as to engage the forward drive sun gear 114 to the axle shaft 108, and        the second change clutch part 140 includes a cylinder 142 disposed in the axle hub 104 positioned at a location corresponding to that of the reverse sun gear 116 in which a reverse piston 146 advances and comes into close contact with the reverse sun gear 116 while compressing a return spring 148 by supply of hydraulic oil into the cylinder 142, and at the same time a clutch plate 145 disposed at the reverse sun gear 116 comes into close contact with frictional plates 147 provided at a second clutch pack 108b extended from the axles shaft 108 so as to engage the reverse sun gear 116 to the axle shaft 108.        